1. Field of the Invention
This invention relates to an IPS mode liquid crystal display using an optical film obtained by laminating a polarizing plate with retardation film, and operating in an IPS mode.
2. Description of the Background Art
Conventionally, as a liquid crystal display, there has been used a liquid crystal display in TN mode in which a liquid crystal having a positive dielectric anisotropy is twisted aligned between substrates mutually facing to each other. However, in TN mode, even when black view is displayed, optical leakage resulting from birefringence caused by liquid crystal molecule near a substrate made it difficult to obtain perfect display of black color owing to driving characteristics thereof. On the other hand, in a liquid crystal display in IPS mode, since liquid crystal molecule has almost parallel and homogeneous alignment to a substrate surface in non-driven state, light passes through the liquid crystal layer, without giving almost any change to a polarization plane, and as a result, arrangement of polarizing plates on upper and lower sides of the substrate enables almost perfect black view in non-driven state.
However, although almost perfect black view may be realized in normal direction to a panel in IPS mode, when a panel is observed in oblique direction, inevitable optical leakage occurs caused by characteristics of a polarizing plate in a direction shifted from an optical axis of the polarizing plates placed on upper and lower sides of the liquid crystal cell, as a result, leading to a problem of narrowing of a viewing angle. That is, a polarizing plate using a triacetyl cellulose (TAC) film generally employed, as a protective film, has had a problem that a viewing angle is narrowed by birefringence that the TAC film has.
In order to solve this problem, a polarizing plate is used in which the shift of a geometric axis of a polarizing plate given when observed from oblique direction is compensated by a retardation film. These polarizing plates are disclosed in JP-A No. 4-305602, and JP-A. 4-371903. In the polarizing plates described in the above-mentioned documents, a retardation film is used as a protective film for a polarizer. With retardation films described in the above-mentioned documents, however, it is difficult to realize a sufficiently wide viewing angle of an IPS mode liquid crystal display.